The invention pertains to a screw-type solid-bowl centrifuge with a driven drum that is supported at both end surfaces and turns about a horizontal axis, and with a transport screw that is rotatably and coaxially arranged in the drum and can be driven at a different speed than the drum, where the drive contains a multistage planetary gear train, the housing jacket of which is connected to the drum jacket, and with the drive shaft of the multistage planetary gear train being connected to the transport screw.
The solid matter is transported to the solid matter discharge at one end surface of the drum due to the differential speed between the drum and the screw.
During the operation, the housing of the multistage planetary gear train rotates about the horizontal axis of rotation of the drum. Since the gear housing is connected to the drum jacket, both components rotate at the same speed.
There exist screw-type solid-bowl centrifuges in which the planetary gear train is arranged between the drum bearings or outside the drum bearing on the drive end together with the drum.
U.S. Pat. No. 3,061,181 discloses a screw-type centrifuge in which the planetary gear train is arranged between the drum bearings together with the drum. In this screw-type centrifuge with a so-called xe2x80x9cinternal gear train,xe2x80x9d the bearing on the drive end can be relatively small, but the distance between the two bearings is increased by the structural width of the planetary gear train.
U.S. Pat. No. 5,403,260 discloses a screw-type centrifuge in which the planetary gear train is arranged outside the drum bearing arrangement. This screw-type centrifuge contains a so-called xe2x80x9cexternal gear train.xe2x80x9d Here, it is disadvantageous that the hub of the housing of the planetary gear train as well as the driven gear shaft must extend through the bearing of the drum on the driven end. At high rotational speeds of the drum and the transport screw, the resulting bearing size can lead to certain problems.
In large screw-type centrifuges, the natural frequency of the drum represents one factor limiting the maximum attainable drum speed. The natural frequency xcfx89 of the drum decreases with the distance L between the drum bearings such that the maximum attainable rotational speed of the drum is-reduced to
xcfx89xcx9c1/L2
For reasons of process technology, a high ratio between the drum length and the drum diameter D, L/D, is usually desired.
Due to the aforementioned problems, the maximum structural length of the drum is reduced by the gear width in screw-type centrifuges with internal gear trains. The high torques occurring in large screw-type centrifuges may make it necessary to provide a multistage planetary gear train such that the width of the gear train is also increased. However, these high torques also result in such large diameters of the driven gear shaft that an external gear train cannot be used due to the disadvantageous bearing size associated with them.
The invention is based on the objective of designing a screw-type centrifuge of the initially mentioned type in such a way that the use of multistage planetary gear trains allows high circumferential speeds of the drum and large drum diameters.
According to the invention, this objective is attained in that the drum bearing on the gear train side is arranged between two stages of the multistage planetary gear train.
In one advantageous embodiment, the housing of the multistage planetary gear train contains a cylindrical intermediate piece within the region of the drum bearing on the gear train side, with the diameter of this intermediate piece being reduced in comparison to the housing parts of the gear train stages. The drum bearing on the gear train side accommodates the intermediate piece as well as a shaft that connects the gear train stages. Consequently, the diameter of the intermediate piece corresponds to the inside diameter of a suitable drum bearing.
In the embodiment according to the invention, at least the last gear train stage with the largest diameter is arranged between the drum bearings together with the drum such that the driven gear shaft with the largest diameter need not extend through the drum bearing on the gear train side and the structural width of the gear only partially affects the distance between the drum bearings. The additional gear train stages can be realized in the form of external gear train stages. The gear train housing must consist of two parts such that the bearing can be mounted within the region of the intermediate piece.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.